The novel is about a lonely young man, Frederick Clegg, who works as a clerk in a city hall, and collects butterflies in his spare time. The first part of the novel tells the story from his point of view.

Clegg is obsessed with Miranda Grey, a middle-class art student at the Slade School of Fine Art. He admires her from a distance, but is unable to make any contact with her because of lacking social skills. One day, he wins a large prize in the football pools. He stops working and buys an isolated house in the countryside. He feels lonely, however, and wants to be with Miranda. Unable to make any normal contact, Clegg decides to add her to his "collection" of pretty, petrified objects, in the hope that if he keeps her captive long enough, she will grow to love him.

After careful preparations, he kidnaps Miranda by drugging her with chloroform and locks her up in the cellar of his house. He is convinced that Miranda will start to love him after some time. However, when she wakes up, she confronts him with his actions. Clegg is embarrassed, and promises to let her go after a month. He promises to show her "every respect", pledging not to sexually molest her and to shower her with gifts and the comforts of home, on one condition: she can't leave the cellar.

Clegg rationalises every step of his plan in cold, emotionless language; he seems truly incapable of relating to other human beings and sharing intimacy with them. He takes great pains to appear normal, and is greatly offended at the suggestion that his motives are anything but reasonable and genuine.

The second part of the novel is narrated by Miranda in the form of fragments from a diary that she keeps during her captivity. Clegg scares her, and she does not understand him in the beginning. Miranda reminisces over her previous life throughout this section of the novel, and many of her diary entries are written either to her sister, or to a man named G.P., whom she respected and admired as an artist. Miranda reveals that G.P. ultimately fell in love with her, and subsequently severed all contact with her. Through Miranda's reflections while confined, Fowles explores a number of philosophical issues, such as the nature of art, humanity and God.

At first, Miranda thinks that Clegg has sexual motives for abducting her, but as his true character begins to be revealed, she realises that this is not true. She starts to have some pity for her captor, comparing him to Caliban in Shakespeare's play The Tempest because of his hopeless obsession with her. Clegg tells Miranda that his first name is Ferdinand (eventual winner of Miranda's affections in The Tempest).

Miranda tries to escape several times, but Clegg stops her. She also tries to seduce him to convince him to let her go. The only result is that he becomes confused and angry. When Clegg keeps refusing to let her go, she starts to fantasize about killing him. After a failed attempt to do so, Miranda passes through a phase of self-loathing. She decides that to kill Clegg would lower her to his level. She refrains from any further attempts to do so. Before she can try to escape again, she becomes seriously ill and dies.

The third part of the novel is narrated by Clegg. At first, he wants to commit suicide after he finds Miranda dead, but after he reads in her diary that she never loved him, he decides that he is not responsible for this outcome and is better off without her. The book ends with his announcement that he plans to kidnap another girl.

In his second book, The Aristos, a collection of philosophical essays, Fowles wrote that he intended the novel to explore the danger of class and intellectual divisions in a society where prosperity for the majority was becoming more widespread, and power (whether by wealth or position) was gained by those intellectually unsuited to handle it.[citation needed]

He further discusses his inspiration for The Collector. He said that the Greek philosopher Heraclitus saw mankind as divided into two groups. The first was a moral and intellectual elite known as the aristoi, or "the good", (not necessarily meaning those of noble birth), and the second was the hoi polloi, or "the many", who were viewed as an unthinking, conforming mass. Fowles wanted readers to understand that "the dividing line should run through each individual, not between individuals."[1]

He wrote,

"I tried to establish the virtual innocence of the many. Miranda, the girl he [Clegg] imprisoned, had very little more control than Clegg over what she was: she had well-to-do parents, a good educational opportunity, inherited aptitude and intelligence. That does not mean that she was perfect. Far from it – she was arrogant in her ideas, a prig, a liberal-humanist slob, like so many university students. Yet if she had not died she might have become something better, the kind of being humanity so desperately need."[1]

Fowles goes on to explain that the purpose of the novel was not to say that a precious elite was threatened by the barbarian hordes. Rather, that people had to face up to an unnecessary brutal conflict based on envy and contempt, and accept that we will never be born equal until The Many can be educated out of a false sense of inferiority and The Few can understand that biological superiority is not a state of existence but rather a state of responsibility. He strongly opposes the view that the idea behind The Collector is a fascist one.[1]

"The Collector", a song inspired by the novel, was written by Sonny Curtis. It was recorded by The Everly Brothers in 1966 and included on their album Two Yanks in England. The song was also recorded by 'The No. 1' band in 1967 on Kapp records (K824/K-10643) b/w "Cracks in the Sidewalk" (Kapp K824/K-10644).

The song "The Butterfly Collector" by The Jam (the B-Side of the 1979 single "Strange Town") was said to be inspired by the book. It was about Soo Catwoman who, upon the implosion of the Sex Pistols, attempted to become part of The Jam's entourage.

The song "Purity" by metal band Slipknot has lyrics related to the novel.

The song "Prosthetics" by Slipknot recount a story similar to that in the novel.

The song "The Collector" by Russian band Deadushki has lyrics related to the novel.

The Smiths song "Half A Person" is thought to be titled after the quote, "Caliban is half a person at the best of times."

The song "International Rock Star" by the Canadian band Stars is loosely related to the plot of the book and features soundbites from the film.

The song "The Man Who Stole A Leopard" by British band Duran Duran (All You Need Is Now album) was inspired by the movie, according to the keyboardist Nick Rhodes.

The basic plot of The Collector: a lonely maladjusted person kidnapping the object of his or her desire, has become a standard plot device of a number of TV shows, ranging from soap operas to crime series. Some more explicit references to John Fowles' book are:

In several cases since the novel was published, serial killers, spree killers, kidnappers, and other criminals have claimed that The Collector was the basis, the inspiration, or the justification for their crimes.[5]

In 1985, Leonard Lake (with help from Charles Chi-Tat Ng) abducted 18-year-old Kathy Allen and later 19-year-old Brenda O'Connor, to satisfy his fantasy of owning his own "Miranda". He is said to have been utterly obsessed with The Collector. Lake described his plan for using the women for sex and housekeeping in a "philosophy" videotape. The two are believed to have murdered at least 25 people, including two entire families. Although Lake had committed several crimes in the Ukiah, California area, his "Operation Miranda" did not begin until after he moved to remote Wilseyville, California. The videotapes of his murders and a diary written by Lake were found buried near the bunker in Wilseyville. They revealed that Lake had named his plot Operation Miranda after the character in Fowles' book.[6]

In 1988, Robert Berdella held his male victims captive and photographed their torture before killing them. He claimed that the film version of The Collector had been his inspiration when he was a teenager.[7]